1. Field of the Invention
The invention relates to Internet Protocol (IP) communication networks, and more particularly to devices for assigning prefixes of network equipments of IP networks, for example routers.
In the present context, the expression “network equipment” means any equipment of an IP network that has to be associated with an IP address in order to be contacted.
2. Description of the Prior Art
The person skilled in the art knows that network equipments such as IP routers have communication interfaces that are connected to links and can be contacted using different IP addresses.
In an IP version N° 6 (IPv6) network, each IPv6 address consists of a network identifier (generally defined by 64 bits) and an interface identifier (generally defined by 64 bits). This kind of address takes the following form, for example: 2001 :1d80 :ab58 :8451 :8454 :1100 :aef0 :8845, in which the leftmost 64 bits (2001 :1d80 :ab58 :8451) constitute the network identifier and the rightmost 64 bits (8454 :1100 :aef0 :8845) constitute the interface identifier.
The interface identifiers are used to differentiate interfaces on the same local link. Each interface identifier of a router is usually determined by the router itself when it is started up, by means of its MAC address.
The network identifiers are used to designate (address) a link on the network. They consist of a network prefix (denoted “/n”), defined by the leftmost more significant 48 bits, for example (in this case denoted, in shortened form, “/48” (n=48)) and defining a family of addresses. The network prefix /n is supplied by the network (generally by a network prefix server) and usually represents 2(64−n) different network identifiers. It therefore serves as a “reserve” for generating other network identifiers.
For example, a global network prefix /48, such as 2001 :458 :1125 ::/48, can be used to define the network identifiers 2001 :458 :1125 :0000 ::/51 through 2001 :458 :1125 :E000 ::/51, which constitute eight (23) prefixes of type /51 that can in turn serve as a reserve for constituting other prefixes of type /54, and so on. In this example, “::” represents a series of successive zeros (0); for example, 2001 :458 :1125 :0000 ::/51 is equivalent to 2001 :458 :1125 :0000 :0000 :0000 :0000 :0000.
In stateless address auto-configuration IPv6 networks, which are defined by Internet Engineering Task Force (IETF) standards RFC 2461 and RFC 2462, each supplies a network identifier to each terminal connected to its interfaces using a router advertisement/router solicitation (RA/RS) mechanism.
To this end, the router must first obtain a network prefix to use as a resource for generating network identifiers for the terminals that are connected to its interfaces. To obtain a prefix, a router may use what the person skilled in the art knows as hierarchical prefix delegation (HPD), as described in particular in the IETF document “draft-bykim-ipv6-hpd-01.txt”, ETRI, 15 Feb. 2004, available at the Internet address http://ieffreport.isoc.org/all-ids/draft-bykim-ipv6-hpd-01.txt.
That mechanism consists first of all in assigning a global network prefix (/n), generally of /48 type, to a single router, called the “root router”, so that it has an addressing space represented by a global network prefix that it can “chop” (or fragment or divide) into (sub-)prefixes of greater length (for example /51) and make available to other “downstream” routers connected via links to its own interfaces. Each downstream router can then in turn chop into (sub-)prefixes of even greater length (for example /54) the (sub-)prefix assigned to it by the (“upstream”) root router, in order to make them available to other downstream routers connected via links to its own interfaces, and so on, thereby progressively constructing a hierarchical delegation tree.
In current networks, the policy on chopping (or fragmenting) (sub-)prefixes is arbitrary because it is fixed once and for all. To be more precise, each (sub-)prefix can be divided into only eight prefixes (8=23, because 51−48=54−51=3, for example); in other words, the length of a sub-prefix is systematically increased by three bits compared to the length of the (sub-)prefix from which it is obtained (for example, a /48 prefix is divided into eight /51 sub-prefixes).
Because of this static and arbitrary division, a router can assign network prefixes (by delegation) only to a fixed number of adjacent routers (eight routers), regardless of the total number of adjacent routers and regardless of the real number of interfaces that each of those adjacent routers includes (and thus regardless of the lengths of the prefixes they really require).
This lack of adaptability, which results from the fact that the routers do not know at least certain configuration characteristics of their adjacent routers, may prove particularly troublesome in certain situations.
An object of the invention is therefore to solve the problem caused by the arbitrary policy on dividing network prefixes into sub-prefixes, as much in hierarchical prefix delegation (HPD) networks as in dynamic host configuration protocol (DHCP) networks.